Hi Theo and Nate,
I took a brief look at this myself, because having an emulated environment would help me with my project. I didn't know then that QemuOpenBoardPkg was an accepted project this year. OvmfPkg is large, I'm unfamiliar with QEMU's codebase and I'm only minimally familiar with Intel's old ICH chipsets (the platform some emulators expose), so I looked at porting QEMU's Q35 + ICH9 support into SimicsOpenBoardPkg. I don't know how you're preparing, but I'd recommend at least a look there: Q35's ICH9 and Simics' ICH10 are fairly similar. There are other QEMU machines, but I can't comment on those.
SimicsOpenBoardPkg can partially boot QEMU with a minimum of changes. It makes it into the DXE phase (where we'd eventually get a shell), but fails to initialise SMM, so it can't load the variable driver in there. Many drivers depend on the variable protocol, including critical UEFI-architecture ones, so the DXE core will assert and hang after printing a bunch of "driver GUID discovered but not loaded" messages. To fix this, the SMM access, maybe SMM control drivers would need to be patched; some register definitions differ between chipsets.
Anyways, I can send you my diff if you'd like, or you're welcome to approach this any way you'd like. SimicsOpenBoardPkg is not a true MinPlatform board because it implements a number of init steps itself rather than using some of MinPlatform's FSP-centric libraries. I'm probably going to skip to the step where I try Frankensteining enough MinPlatform code in to suffice my testing.